Fix client area calculation

When the draggable_regions->getBounds() has smaller width than
the widget's width, the inset decreases the top regions of the
widget but inversion is computed against draggable_regions width,
so it misses some additional client areas asides the draggable
regions.

Instead, the inversion needs to be computed against the areas
decreased by the inset.

Bug: 939094
Test: manually
Change-Id: Ia1b509b6ec5cf1ba10b44919b1da73eb03942608
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1509097
Commit-Queue: Jun Mukai <mukai@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638709}

chrome/browser/ui/views/apps/chrome_native_app_window_views_aura_ash.cc

@@ -361,8 +361,12 @@ void ChromeNativeAppWindowViewsAuraAsh::UpdateDraggableRegions(
     gfx::Insets insets(draggable_region->getBounds().bottom(), 0, 0, 0);
 
     // Invert the draggable regions to determine the additional client areas.
+    // Inversion should be computed for the difference between the inset area
+    // and the draggable_region -- draggable_region->getBounds() could have
+    // smaller width than widget's width.
     SkRegion inverted_region;
-    inverted_region.setRect(draggable_region->getBounds());
+    inverted_region.setRect(0, 0, widget()->GetWindowBoundsInScreen().width(),
+                            draggable_region->getBounds().bottom());
     inverted_region.op(*draggable_region, SkRegion::kDifference_Op);
     std::vector<gfx::Rect> additional_client_regions;
     for (SkRegion::Iterator i(inverted_region); !i.done(); i.next())